Torsional disturbances in drivelines, which can include continuous angular oscillations, compromise the performance and reliability of driveline components. For example, the torsional vibrations can produce damage, excessive wear, and noise in the driveline components.
Flexible torsional couplings between driving and driven members of the drivelines can smooth torque variations from engine disturbances, such as engine firing impulses, and reduce associated resonances and other torsional vibrations within the loaded drivelines. The flexible torsional couplings can incorporate elastomers or other resilient elements that provide a flexible coupling between the driving and driven members. The elastomers exhibit a given spring rate function by allowing angular deflection between the driving and driven members as a function of the torque applied across the elastomer.
For purposes of dampening vibrations, particularly in the drivelines of heavy-duty vehicles such as tractors and construction vehicles, different spring rate functions are more effective for different torque loads and speeds. A flexible dual-rate coupling disclosed in U.S. Pat. No. 5,573,462 to Sweeney et al. of Lord Corporation, the assignee of the current invention, includes elastomer couplings in series to provide different dampening spring rates for different torque ranges. The first elastomer, which exhibits a relatively low spring rate, is effective for transferring torque while dampening vibrations through a first range of torque values, and the second elastomer, which exhibits a relatively high spring rate, is effective for transferring torque and dampening vibrations through a second range of torque values. The two ranges are delineated by a snubber device that limits the angular deflection through which one of the elastomers is allowed to operate, while the other elastomer continues to operate for transmitting torque. This patent to Sweeney et al. is hereby incorporated by reference.